Detergent compositions, especially low density detergent compositions often contain high levels of sulphates. A problem encountered with these detergents can be the poor solubility properties of one or more components in the detergent. A consequence of this in a typical washing process can be poor dispensing of the product, either from the dispensing drawer of a washing machine, or from a dosing device placed with the laundry inside the machine. This can reduces the effectiveness of the powder. This is a particular problem at low water pressures and/or at lower washing temperatures.
The prior art teaches various ways to improve the solubility of high bulk density detergent compositions. WO95/14767 relates to the poor dispensing of high density, non-spray-dried detergent powders, and discloses the use of a citric acid salt which has a Rosin Rammler particle size of less than 800 microns. WO94/28098 discloses a non-spray-dried detergent powder comprising a combination of an ethoxylated primary C8-18 alcohol, an alkali metal aluminosilicate builder and 5 to 40wt % of a water-soluble salt of a citric acid.
The use of effervescence to improve the dispersability of granular materials has been used extensively in pharmaceutical preparations. The most widely used effervescent system in this respect is citric acid in combination with bicarbonate. This effervescent system has also been described for improving the dispersabality of pesticidal compositions for controlling water-bore pests, e.g. GB-A-2,184,946.
It has now been found that particularly in low density detergent compositions, comprising high levels of sulphate, poor dispersing can lead to insolubility/precipitation of certain components (present in the washing water) onto the fabrics in the wash and onto the washing machine. In particular, it has been found that calcium and magnesium carbonate and limesoaps, formed by the water hardness, can precipitate onto the fabric. It has been found that this can even occur when builders (which are traditionally employed in detergents to counter the adverse effect on detergency of water hardness ions) are present.
Without wishing to be bound by theory, the Applicants believe that this is due to increased ionic strength, due to the high level of sulphates present in the washing water. The Applicants have now found that this problem can be solved by the use of a specific dispersing aid. It has been found that the precipitation of various components, such as magnesium and calcium carbonates and lime soaps, can be reduced in a low density detergent composition containing sulphate, an alkali source and incorporating a dispersing aid which is an acid source, can react with the alkali source to produce a gas, and which can also act as a water-soluble dispersant or builder material.
It is believed that the reaction of the acid source and the alkali source which produces gas (preferably carbon dioxide) firstly helps the dispersion and dispensing of the detergent, reducing deposition of (detergent) components on fabrics and the machine. In addition, builder materials will be dispensed more effectively so that calcium and magnesium ions are rapidly contacted with builder material, thereby quickly and effectively reducing the free calcium and magnesium in the water so that the formation of undesirably precipitates is substantially reduced. Furthermore, once in the wash water acid is de-protonated and the base form of the acid can act as a dispersant or builder, further reducing the free calcium and magnesium in the water and further reducing the formation of undesirable precipitates.
All documents cited in the present description are incorporated herein by reference.